Formation of the five-membered zirconacyclocumulene Cp2Zr(η4-Bu~tC4Bu~t) and the binuclear zirconocene butatrienyl complex Cp2(Bu~n)Zr(Bu~tC4Bu~t)Zr(Bu~n)Cp2 in the reaction of the Negishi reagent with 1,4-di(tert-butyl)butadiyne

摘要

We have recently reported the synthesis of di-n-bu-tylhafnocene Cp2HfBu~n2 (1), being a hafnium analog of the Negishi reagent Cp2ZrBu~n2, which is widely used in organometallic chemistry of zirconium as a source of highly reactive "Cp2Zr" (see Refs 3 and 4). Compound 1 was synthesized by the reaction of Cp2HfCl2 with n-butyl-lithium and turned out to be much more stable than Cp2ZrBu~n2. Unlike its zirconium analog, which rapidly decomposes already at low temperatures, hafnium complex 1 loses the butyl groups and generates "Cp2Hf" only at 100 °C, which provides new potentialities for organometallic synthesis. In fact, we showed that the use of compound 1 as a source of "Cp2Hf "in the reactions with 1,4-disubstituted butadiynes RC≡C-C≡CR (R = Bu~t, Ph, and SiMe3) makes it possible to synthesize various hafna- cycles in good yields. Particularly, the hafnacyclocumu-lene complex Cp2Hf(η~4-Bu~tC4Bu~t) was synthesized, which is the first example of the structurally characterized five-membered hafnacyclocumulene. Taking into account these data, we decided to study the reaction of the Negishi reagent with the above-mentioned diynes. The results obtained for 1,4-di(tert-butyl)butadiyne are presented in this work.